1. Field of the Invention
The present invention relates to an image display device, and more particularly, to an image display device using a light emitting element.
2. Description of the Related Art
In recent years, image display devices using a light emitting element, such as organic electroluminescent (EL) display devices, are being actively developed. Pixel circuits constituting the image display device each include a light emitting element, a drive transistor for controlling the amount of current to be supplied to the light emitting element, and a storage capacitor for applying a potential to a gate electrode of the drive transistor. The drive transistor is generally formed by a thin film transistor, which is a type of an electric field effect transistor. In order to prevent degradation in image quality caused by a fluctuation in threshold voltage among the drive transistors, an auto-zero operation is performed. In the auto-zero operation, the gate electrode and a drain electrode of the drive transistor are connected to each other to cause a current to flow until the current stops flowing naturally so that a potential difference corresponding to the threshold voltage is generated between the gate electrode and a source electrode of the drive transistor, and then a potential difference that reflects the potential difference corresponding to the threshold voltage is stored in the storage capacitor. In order to perform the auto-zero operation, it is necessary to previously set a potential of the gate electrode of the drive transistor in a given range. A known method for realizing the preset operation is to supply a potential of a data line to a node to which the gate electrode of the drive transistor is connected.
FIG. 14 is a diagram illustrating an example of the pixel circuit of the conventional image display device. The image display device includes a data line DAT, a power supply line PWR, a selection control line SEL, a lighting reset control line CTL, an initial voltage control line CLR, and the plurality of pixel circuits. The pixel circuits each include a light emitting element IL, a drive transistor TRD, a storage capacitor CP, a selection switch SWS, a lighting control switch SWI, a reset switch SWR, and an initial voltage supply switch SWL. The drive transistor TRD has a source electrode connected to the power supply line PWR and a gate electrode connected to one end of the storage capacitor CP. The selection switch SWS is provided between another end of the storage capacitor CP and the data line DAT, and controlled by the selection control line SEL. A drain electrode of the drive transistor TRD is connected to one end of the lighting control switch SWI, one end of the reset switch SWR, and one end of the initial voltage supply switch SWL. The lighting control switch SWI has another end connected to an anode of the light emitting element IL. The reset switch SWR has another end connected to the gate electrode of the drive transistor TRD. The initial voltage supply switch SWL has another end connected to the other end of the storage capacitor CP.
In a first period before the auto-zero operation is performed, the selection switch SWS, the initial voltage supply switch SWL, and the reset switch SWR are turned ON. Accordingly, a potential of the gate electrode of the drive transistor TRD becomes a potential of the data line DAT. On this occasion, the data line DAT supplies such a potential that turns ON the drive transistor TRD. Next, in a second period in which the auto-zero operation is performed, the initial voltage supply switch SWL is turned OFF. Japanese Patent Application Laid-open No. 2005-91724 discloses an example of the above-mentioned conventional organic electroluminescent (EL) display device.